This invention pertains to power conversion apparatus, and specifically to apparatus which enables the conversion of single-phase AC power to three-phase AC power. More particularly, it pertains to such a system wherein the AC frequency required by a selected three-phase load is the same of that as an available single-phase source.
There are many circumstances where it is required, or at least desired, to operate a three-phase load, such as a three-phase motor, in a facility where only, for example, conventional 120-volt single-phase power is available.
Conversion circuitry which has been proposed in the past to accomplish the task of "matching the load to the source" is typically quite complex and expensive, in that it usually employs a large number of relatively expensive power switches (switching transistors) to accomplish the required conversion. In most cases, six such switches are employed.
An important object of the present invention is to provide apparatus which is capable of performing the kind of conversion just mentioned utilizing a minimum number (no more than two) of such switches.
This surprising reduction in the number of power switches required to effect conversion results from the recognition that, in a sense, the two available output terminals of single-phase AC power can, in effect, each be connected directly to a different one of the input terminals in the selected load, with the voltage supply to the third load input terminal being derived from the single-phase source, and supplied through only two power switches operated under computer or microprocessor control. Put another way, the invention rests, in strong measure, on the recognition that, in the setting described, high-speed power switching is not required in the provision of power to two of the three input terminals in a three-phase load.
The advantages of such a recognition are immediately apparent. The resulting circuitry is greatly simplified, and its costs substantially reduced, in comparison with similar characteristics of the conventional single-phase to three-phase conversion systems.
These and other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.